Poor indoor air quality in homes and office buildings has been recognized as a primary factor which leads to respiratory problems in people. Radon is a primary contributor and levels above four pico-curies per liter (4 pCi/l) have been statistically shown to increase the risk of cancer in individuals. Current EPA efforts are directed to reducing levels of radon below 4 pCi/l and have set target levels of 0.4 pCi/l which is approximately the level in atmospheric air.
Radon gas, which is a radioactive decay by-product of radium, constantly seeps from subterranean radium deposits and out through the surface of the earth's crust, into the atmosphere surrounding the earth. It has a relatively short half-life, in the order of four days. Thus, the radon gas concentration never reaches significant levels upon escaping into the earth's atmosphere. Without confinement, radon gas does not reach sufficient concentration levels, e.g., above 4 pCi/l to pose a human health hazard. When an enclosed structure, such as a building, e.g. a dwelling, or office building, is located in an area of significant radon effluence, as often exists in various parts of the United States, the radon seeps into the structure through cracks or other openings in parts of the foundation, basement or other parts of the building that are in contact or near contact with the earth. If there is an inadequate exchange of interior and exterior air within the building, significant radon concentrations can develop within a building, which are above current governmental limits, e.g., above 4 pCi/l.
There have been significant developments in methods for the detection of radon in an enclosed building or structure and for removal of radon from such building. Representative patents illustrating systems to purify indoor air to remove these various impurities in buildings such as homes, office buildings, etc. include U.S. Pat. Nos. 4,764,187; 4,801,800; 4,849,111; 6,440,196; 6,342,191; 6,338,830; and 6,658,894; all of which are incorporated herein by reference.